World War I was a direct result of a tangled system of secret alliances. Beginning after the unification of Germany in 1871, many European nations began secretly allying themselves with each other. Starting with the Dual Alliance between Austria-Hungry and Germany in 1879, the nations of Europe allied themselves in mutual protection pacts in such a way that if any one nation became the target of aggression, all of Europe would be pulled into war. That act of aggression occurred in Bosnia in 1914 when a young serb, Gavrilo Princip, assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne. Austria-Hungry declared war on the nation of Serbia soon after. Within a year, Austria-Hungry, Germany and Italy had allied themselves against France, Britain, Russia and the Ottoman Empire.

The after-effects of the war are numerous. Four empire disappeared; Austria-Hungry, the Ottomans, Germany and Russia. Four age-old royal lines were shattered; the Hapsburgs, Romanov’s, Hohenzollerens and the Ottman turks. Of the 60 million soldiers mobilized during the war, 8 million were dead, 7 million were disabled in some way and 15 million were seriously injured. 15% of German’s men aged 18-40 were gone, as were 17% of Austria-Hungry. A global famine also came after the war, killing 100,000 people in Lebannon and 10 million in Russia! One of the most important effects was that Germany was saddled with a huge war debt that bankrupted the nation and provided fertile ground for the rise of Hitler and the Nazi's, so one could argue World War I caused World War II

There were some positive effects as well. There were vast improvements in the way armies cared for wounded soldiers and veterens. Mental health care for soliders with PTS syndrome was beginning to be introduced and the League of Nations was formed. While the League itself proved to be ineffective, it was the precursor to the United Nations, a much more effective international organization.

Also, it is often said that the Treaty of Versailles only prolonged the other half of the war, World War II, because it gave reasons for Germany to rise up again and try to take over Europe. Truly, the two world wars could be considered one war with a prolonged truce in the middle.

World War I was caused by a variety of things. Militarism and war fever were big: the European nations were growing ever more powerful, and the armed forces of many of these countries (i.e. Britain, Russia, Germany.

Another cause was the alliance system, conjured up by the German Otto von Bismarck. The alliance system entangled the involved countries with treaties and agreements that often contradicted each other, causing conflict between a few countries to escalate into a world war.

Imperialism also posed a problem, as the most powerful nations in the world were scrambling to colonize and militarize then-under-developed nations in Africa, South America, Asia, and the Pacific. With nearly all of the great military powers rubbing shoulders to build up their own empires, a confrontation was inevitable.

Yet another cause for World War I was the assassination of the Austro-Hungarian archduke Franz Ferdinand. The archduke was killed while in Sarajevo, and the killer was from a secret organization known as the "Black Hand". Austrian officials put the blame on Serbia for the death of their archduke, and eventually declared war. Because of the alliance system discussed above, the other European nations were roped into the conflict, causing it to become a world war.

Mobilization of armed forces was another more immediate cause of World War I. Russia, in defense of Serbia, mobilized its troops on the border of Germany and Austria-Hungary. (Germany was an ally of Austria-Hungary.) Germany was already plotting to invade Russia through its Schlieffen Plan, which would require the German army to march through Belgium to invade France, take Paris, then swing around and head for Russia. This Schlieffen Plan was supposed to prevent a war in which Germany would have an enemy on both sides by disabling the French. The Schlieffen Plan, obviously, failed.

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The results of the Great War were almost as numerous as the causes. By its end in 1918, American had entered the war and Russia had withdrawn (due to revolutionary uprisings). Woodrow Wilson, the American president at the time, proposed peace through his Fourteen Points. Unfortunately, the Fourteen Points were not accepted by the European nations.

The First World War ended officially on 28 July 1919, with the signing of the Treaty of Versaille. The treaty blamed Germany for the war and required that nation to pay the most reparations, to give up its overseas property, and to demilitarize at once.

Another huge result of the Treaty of Versaille was the changing of borders in Europe. France was to gain back Alsace and Loraine, which had previously been taken by Prussia (Germany) in the Franco-Prussian War in the 1870s. Germany also lost a lot of land, which was gained by smaller, neighboring countries such as Denmark, Czechoslovakia, and Belgium. Germany also lost the "Polish Corridor", which was (of course) given to Poland. In addition to this, the Rhineland was to be occupied for 15 years as a buffer state between France and Germany. Austria-Hungary was also fragmented into many small countries, leaving it permenantly weakened. In addition to this, the Ottoman Empire had crumbled during the war, leading to newly "independent" Middle Eastern nation-states (which were quickly snatched up by Britain, France, etc.)

The end of the war also caused a temporary economic bubble, which soon popped and the Great Depression began.